1. Field of the Invention
The present invention relates to crossed-field amplifiers. More precisely, the present invention relates to a preferentially cooled crossed-field amplifier using a combination of backwall cooling and internal anode vane cooling to cool the anode vanes.
2. Description of the Related Art
Crossed-field amplifiers have been known for several years. These amplifiers are usually employed in electronic systems that require high power outputs, such as radar systems. Typically, crossed-field amplifiers have a secondary emission type cathode that operates on a principle of priming electron bombardment of the cathode emitting surface causing secondary electrons to be emitted. The secondary electrons then give up energy to an RF signal traveling on an anode vane structure that surrounds the cathode, thus increasing the power of the RF signal.
A problem with such high power amplifiers is the efficient removal of heat from the anode structure. When electrons leave the cathode of the crossed-field amplifier in a direction perpendicular to the magnetic field, the field causes a force to act at right angles to the electron motion. The electrons then spiral into orbit around the cathode instead of moving colinearly with the electric field. Most of the electrons gradually move toward the anode, giving up potential energy to the RF field as they interact with the anode slow-wave structure. But to impart this action, there must be high-electron discharge that generates heat build-up. The heat build-up increases as the RF wave propagates towards the RF output. As a result, the output vanes, e.g., those vanes nearest the RF output, typically must dissipate 2 to 3 times the power dissipated by an average vane.
To cool the anode, in conventional crossed-field amplifiers, coolant fluid is pumped directly adjacent to the cathode. An example of a crossed-field amplifier that is liquid cooled is disclosed in U.S. Pat. No. 4,700,109, issued Oct. 13, 1987, to G.R. MacPhail.
In double helix coupled vane crossed-field amplifiers, known in the art, oil or water coolant is supplied to the base of the anode vanes via one or more backwall channels. This standard backwall cooled anode design is sometimes inadequate to meet system requirements. In some cases, the anode vanes becomes too hot and the protective coating on the vane tips burns off.
The above-referenced copending application proposed solving this problem by incorporating a U-shaped tube into each individual vane. This circulated the coolant closer to the vane tips, helping to reduce vane tip temperature. In certain high power applications, however, this type of vane cooling required a high pressure cooling system in order to force coolant through the small diameter tube disposed in each vane. Pressure was approximately 100 psig, well above the 35 psig required in normal application. Thus, in order to better the maximum duty capabilities in such high power applications, it is necessary to further improve vane cooling and reduce cooling system pressure.
Accordingly, a need presently exists for a lower pressure cooling system which improves cooling of the output vanes of a standard double helix coupled vane crossed-field amplifier.